Joke of the month!

(Teacher Nigel says this is one of his best jokes. If you have a better one please hand it to us in the Internet room)
Situation: At the breakfast table
John: I don’t want to go to school today!
Mary: Why not?
John: Well the students don’t like me.The teachers don’t like me,and even the cleaning lady doesn’t like me!
Mary: Well,you must go!
John: Why?
Mary: Well for one you are 40 years old and for the other thing, you’re the headmaster!